连续波DF/HF化学激光器收缩段氦气膜注入式新型喷管的理论研究

Theoretical Investigation of Nozzle with Helium Film Injection at the Converge Section in CW DF/HF Chemical Laser

连续波(CW)DF/HF化学激光器喷管中一般有近20%的氟原子复合为氟分子,这是影响激光器抽运效率和激射强度的重要因素。尤其是壁面复合反应对氟原子的损耗占主要地位。通过喷管型面设计等方法减少氟原子的复合效果不共明显。结合航空领域中气膜冷却方案设想通过在喷管收缩段位置处注入氦气层,隔离氟原子气流与喷管壁面,实现降低氟原子损耗的目的,同时保护喷管壁面及喉道部分避免过度烧蚀。数值模拟结果显示此方法可同时实现对喷管壁面的冷却保护和有效提高氟原子的冻结效率。但注入的氦气将占据部分气流通道,影响主气流在喷管中的传输。在主气流属性保持不变的情况下,喷管出口平面(NEP)上氟原子绝对流率将下降。针对引入的不足,提出了几种改进方案。

About 20% fluorine atoms recombine to fluorine molecules in continuous wave（CW ）DF/HF chemical laser＇s nozzle, and it is one of the most important factors influencing the bumping efficiency and lasing intensity of lasers. The fluorine atoms loss is caused mainly by wall recombination. Nozzle contour design does not have an obvious effect on reducing it. Combining the gaseous film cooling used in aerospace realm, a new kind of nozzle is designed by injecting helium film from nozzle＇s converge section. The film is estimated to be a separating layer between the main stream and nozzle wall which can reduce fluorine atoms loss, protect the wall, and throat region from ablation. The numerical results show that the protection and frozen efficient are obvious. The helium film occupies part of the stream channel, which influences the main stream＇s transportation. The absolute mass flow rate of fluorine atom falls at nozzle exit plane（NEP） if the main stream＇s property keep constant. Several methods are presented to improve the design＇s inherent shortage.